1. Technical Field
This invention relates to the setting of blind rivets. More particularly, this invention relates to a blind rivet setting system in which a blind rivet is first set and then the correctness of the breaking point of the mandrel stem is verified.
2. Discussion
Rivets are widely used to firmly fasten together two or more components of little susceptibility to loosening and thus to produce a tight joint at a low cost.
The setting of the common rivet is accomplished when one end of the rivet is mechanically deformed to create a second head. The blind rivet is a special class of rivet that can be set without the need for mechanical deformation by a separate tool to create the second head. Special blind rivet setting tools are used for setting these types of rivets. Examples of setting tools may be found in U.S. Pat. No. 3,713,321 issued on Jan. 30, 1973 to Gabriel for RIVET GUN, U.S. Pat. No. 3,828,603 issued on Aug. 13, 1974 to (Scheffield) et al. for riveting apparatus, and U.S. Pat. No. 4,263,801 issued on Apr. 28, 1981 to Gregory for HYDRAULIC RIVETER. These tools provide various approaches to setting rivets including setting by hydraulic and pneumatic power.
A relatively sophisticated version of a blind rivet setting tool is disclosed in U.S. Pat. No. 4,744,238 issued on May 17, 1988 to Halbert for PNEUMATIC RIVET SETTING TOOL. This setting tool includes a rivet feed mechanism, a rivet magazine and sequencing controls providing cycle-through operation that utilizes pneumatic logic control. A self-diagnosing blind rivet tool is disclosed in U.S. Pat. No. 4,754,643 issued on Jul. 5, 1988 to Weeks, Jr. et al. for METHOD AND APPARATUS FOR AUTOMATICALLY INSTALLING MANDREL RIVETS. This patent is directed to an automated and semi-automated rivet installation system that has the ability to diagnose selected tool conditions and to convey information on the conditions to the operator. Monitored conditions include the rivet placement within the tool, mechanism positions, and air pressure conditions.
While the prior art apparatus have overcome some of the difficulties inherent in the setting of blind rivets, a remaining difficulty common in the setting of blind rivets has to do with the mandrel and its associated stem. The blind rivet conventionally includes a frangible tubular body and an elongated mandrel. The mandrel includes an enlarged head and a stem extending rearwardly of the head through the frangible tubular body. A weakened area is selectively formed along the length of the mandrel stem so as to provide a breaking point. When the rivet setting tool pulls on the mandrel stem, the stem is intended to break from the mandrel head at this preselected weakened point, thereby assuring that the tubular body is correctly deformed and the rivet properly set. If the mandrel stem does not break at this preselected point, the spent stem will be too short or too long. Either situation results in an incorrect rivet set.
Accordingly, knowledge concerning the length of a particular spent stem would provide the operator with useful information about the correctness of the rivet set. However, while stem length is an important characteristic in assuring a correctly set rivet, measurement of the spent stem is not a simple task. Unless the length is so improper as to be plainly obvious, simple visual analysis is virtually useless in that even a relatively minor variation in stem length from the predetermined ideal length could result in an improperly set rivet. Actual measurement of each spent stem is thus required to assure a proper rivet set. However, it would be entirely impractical for the operator to physically measure each spent mandrel stem against an ideal length.
Accordingly, there is still a need for a system by which a blind rivet may be first set, the correctness of the mandrel stem breaking point be efficiently measured, and the actual length be compared against a predetermined desired length for set verification.